This invention relates to a light-emitting and light-sensing diode array device, a light-emitting and light-sensing diode, and to fabrication methods thereof.
Linear arrays of light-emitting diodes (commonly referred to as LEDs) are used in printers and copiers to form latent electrostatic images by illuminating a photosensitive medium, typically a revolving drum. To function as light emitters, the diodes are forward-biased. If they are reverse-biased, however, the same diodes can function as light sensors for use in scanning documents. This offers an economical way to build a device that can operate in various modes: for example, as a printer, scanner, copier, and facsimile machine. Examples of such devices can be found in the prior art.
The present invention addresses two problems that occur when an array of LEDs is also used for light sensing. The first problem is that the sensitivity is low. The second problem, which can also occur in arrays of purely light-sensing diodes, is that the sensitivity is non-uniform.